Most residential roofs provide some type of attic or airspace that can accommodate an effective radiant barrier system. In new residential construction, it is fairly easy to install a radiant barrier system. The following images show five possible locations for the installation of an attic radiant barrier system.
Location 1, where the radiant barrier material is pre-applied to the roof decking (you can purchase radiant barrier decking), is appropriate if you are building a new house or if you are replacing your roof decking for other reasons.
Location 2 may offer advantages to the builder during construction of a new house. Before the roof sheathing is applied, the radiant barrier is draped over the rafters or trusses in a way that allows the product to droop 1-1/2 to 3 inches between each rafter.
In Locations 3 and 4, the radiant barrier is attached to either the faces or bottoms of the rafters or top chords of the roof trusses. Locations 3 and 4 may be used with either new construction, or with retrofit of an existing house.
In Location 5, the radiant barrier is laid out on the attic floor over the top of existing attic insulation. (See the discussion for important information about performance problems associated with dust for this option.)
With either Location 2, 3 or 4, the space between the roof sheathing and the radiant barrier provides a channel through which warm air can move freely. For any of the radiant barrier locations (and for attics without radiant barriers), ideal venting would provide equal areas on intake (soffit) and exhaust (gable or ridge) vents. For proper air flow, with a roof-mounted radiant barrier, a gap of approximately 3 inches should be left between the radiant barrier and the insulation, and a gap of at least 6 inches should be left near the ridge. Both of these gaps should be left for attics with either ridge or gable venting.
Even though some testing shows that a brand new application in location 5, the attic floor, will work better than the roof applications, there are several drawbacks to this location. The attic floor application is most susceptible to accumulation of dust, while downward facing reflective surfaces used with many roof applications are not likely to become dusty. After a long enough period of time, a dusty attic floor application will lose much of its effectiveness. Predictive modeling results, based on testing, suggest that a dusty attic floor application will lose about half of its effectiveness after about one to ten years. For this location, moisture issues must also be considered. The floor location is not appropriate when a large part of the attic is used for storage, since the radiant barrier surface must be exposed to the attic space. Also, kitchen and bathroom vents and recessed lights should not be covered with the radiant barrier. If a one-sided radiant barrier is laid on top of the insulation with the reflective side facing down and touching the insulation, the radiant barrier will lose most of its effectiveness in reducing heating and cooling loads.